Fuel injection valve

ABSTRACT

A fuel injector, especially an injector valve for fuel injection equipment in internal combustion engines, includes a piezoelectric or magnetostrictive actuator and a valve closing body, operable by an actuator with the aid of a valve needle, which cooperates with a valve seat surface to form a sealing seat, and a valve housing. The actuator is prestressed by a compression spring and, together with this, is surrounded by an actuator housing which is supported by fluid at both its ends.

FIELD OF THE INVENTION

The present invention relates to a fuel injector.

BACKGROUND INFORMATION

Ordinarily, changes in length of a piezoelectric actuator in a fuelinjector are compensated for by the influence of temperature usinghydraulic devices or by choosing suitable material combinations.

European Published Patent Application No. 0 869 278 describes a fuelinjector in which the longitudinal change of the actuator is compensatedfor by an appropriate material combination. The fuel injector as in thisdocument has an actuator, positioned in an actuator chamber, which isconnected with form locking to a pressure shoulder via which theactuator acts upon the valve needle in opposition to the force of apressure spring. The actuator is supported at one end on a pressureplate, and at the other end on a control element. During operation ofthe actuator, the valve needle is activated in the direction ofspray-off.

In the document named, compensation for the longitudinal change of theactuator, caused by temperature, is achieved by a plurality ofcompensation discs positioned between the pressure plate and the endface of the actuator. These have a temperature expansion coefficientcorresponding with opposite sign to that of the actuator element. Duringa shortening of the actuator caused by rising temperature, thecompensation discs expand, and thereby compensate for the thermallongitudinal change of the actuator.

This design has a disadvantage above all in connection with cost ofmanufacture, having relatively high costs conditional especially on thechoice of materials (e.g. INVAR). The compensation for longitudinalchanges by hydraulic devices is known, for instance, from EuropeanPatent 0 477 400. With designs of this kind, the fundamentaldisadvantage is that large volumes of liquid have to be displaced, and,because of that, there is a greater tendency to cavitation.

SUMMARY OF THE INVENTION

The fuel injector according to the present invention on the other hand,has the advantage of simple construction of the component parts, from astandpoint of production engineering. This guarantees a fail-safe andprecise method of operation of the fuel injector. Of particularadvantage are the liquid support on both sides and the low dampingvolume for avoiding cavitational damage.

Especially of advantage are the encapsulation and prestressing of theactuator, since the quasi-static thermal linear deformation of theactuator does not have to be compensated for by costly materialcombinations, but is compensated for by a change in initial stress ofthe compression spring. Thereby, the overall length of the actuatorhousing is not influenced by thermal changes in length. For that reason,only a change in position of the actuator housing relatively to thevalve housing still has to be compensated.

Sealing the actuator housing from the valve housing has the advantagethat the actuator cannot be attacked by the chemically aggressive fuel.

The use of fuel as hydraulic medium is of advantage, since leakagelosses can be compensated permanently by fuel supply.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an axial section through an exemplary embodiment of a fuelinjector according to the present invention.

DETAILED DESCRIPTION

In an axial section, FIG. 1 illustrates an exemplary embodiment of fuelinjector 1 according to the present invention. This is about a so-calledtop feed injection valve having central fuel supply via a fuel inlet 28which opens toward the inside.

In an actuator housing 2, an actuator 3 of ring-shaped design, having acentral hollow recess 29 and being made of disc-shaped piezoelectric ormagnetostrictive elements 4 and a compression spring 5, are located. Theactuator 3 is operated by an external voltage source via a plugconnection 12. To make it simple, only one single contact 13 is shown inFIG. 1. The actuator housing is closed at its ends by a first outerflange 6 and a second outer flange 7, which are sealed from a valvehousing 10 surrounding the actuator 3 by a first sealing element 8 and asecond sealing element 9.

The first outer flange 6 includes a first disc 31 and a first sleeve 32.The first disc 31 lies at a first end face 24 of actuator 3. The secondouter flange 7 includes a second disc 33 and a second sleeve 34. Thesecond disc 33 abuts a first end 26 of compression spring 5. A secondend face 25 of actuator 3 and a second end 27 of compression spring 5are supported on a middle flange 11. Actuator 3 is held under prestressby compression spring 5 via middle flange 11.

Middle flange 11 is preferably connected with force-locking to anoperating body 15 by a weld 14. The operating body 15 is located in thecentral recess 29 of actuator 3, and is in contact, via extension an 35,with a valve needle 17, at which a valve closing body 30 is formed.During lifting off of the valve closing body 30 from a valve seatsurface 18 of a valve seat body, fuel is sprayed off through a spray-offopening 19. Operating body 15 is supported on the inlet side on a returnspring 20 and grips from behind with its spray-off side extension 35 aflange 36 of valve needle 17. Between flange 36 of valve needle 17 andoperating body 15 a spring 16 is clamped. During the closing movement,operating body 15 can swing through with respect to valve needle 17, sothat only the inert mass of valve needle 17 strikes against valve seatsurface 18. This avoids bounce pulses. The fuel flows through an innerhollow recess 37 of the operating body 15, transverse borings 38upstream from flange 36 and at least one passage 39 to the sealing seat.

Between first sleeve 32 of first outer flange 6 and valve housing 10there is a first damping chamber 21. Between the second sleeve 34 ofsecond outer flange 7 and valve housing 10 there is a second ring-shapeddamping chamber 22. Damping chambers 21 and 22 are in contact with fuelinlet 28 via guide slot 23 partially throttled, and are thereby filledwith fuel as damping medium. They buffer actuator housing 2 againstvalve housing 10. When needed, damping medium is supplied or given offvia guide slot 23. Actuating housing 2 is thus axially freely, slidinglymovable in valve housing 10, under oppositely changing volumes in firstdamper chamber 21 and second damper chamber 22.

When an electrical operating voltage is connected to actuator 3 of fuelinjector 1 according to the present invention shown in FIG. 1, thedisc-shaped elements 4 of actuator 3 expand, whereby middle flange 11 ismoved counter to the flowing direction of the fuel. Compression spring 5is further pressed together, counter to the already presentprestressing. Valve closing body 30 lifts off valve seat surface 18 andfuel is sprayed off through spray-off opening 19.

Because of the great operating frequency of actuator 3 during theoperation of fuel injector 1 according to the present invention in aninternal combustion engine, the damping medium between the outer flanges6 and 7 of actuator housing 2 and valve housing 10 in damping chambers21 and 22 behaves as an incompressible fluid, since the expansion ofactuator 3 during its operation occurs too rapidly for the dampingmedium to escape through guide slot 23.

A fuel injector 1 experiences great temperature fluctuations duringoperation. On the one hand, the entire fuel injector 1 heats up throughcontact with the combustion chamber of an internal combustion engine,and on the other hand, local temperature effects appear, for instance,from the power loss during deformation of piezoelectric actuator 3 orfrom electrical charge movement. This results in a thermal lengthreduction of disc-shaped elements 4, since piezoelectric ceramics havenegative temperature expansion coefficients, that is, they contractwhile heating up and expand while cooling.

Such a shortening of actuator 3 by heating is compensated insideactuator housing 2 by the expansion of prestressed compression spring 5.The shortening of actuator 2 leads to a lengthening of compressionspring 5. Since middle flange 11 is stopped at operating body 15 by weld14, the change of length of actuator 3 results in a positional change ofactuator housing 2. This positional change of actuator housing 2 isopposed by the fluid storage of actuator housing 2 within valve housing10, since, during quasi-static positional changes of actuator housing 2relatively to valve housing 10 through temperature influences, themovement of actuator housing 2 takes place so slowly, that damper mediumcan escape through guide slot 23 or can continue flowing.

The present invention is not limited to the illustrated exemplaryembodiment, but can also be carried out in a multitude of other methodsof construction of fuel injectors.

What is claimed is:
 1. A fuel injector, comprising: one of apiezoelectric actuator and a magnetostrictive actuator; a valve needle;a valve seat surface; a valve closing body that is operable by the oneof the piezoelectric actuator and the magnetostrictive actuator with theaid of the valve needle, the valve closing body cooperating with thevalve seat surface to form a sealing seat; a compression spring forprestressing the one of the piezoelectric actuator and themagnetostrictive actuator; and an actuator housing supported at bothends thereof by a fluid and for surrounding the compression spring andthe one of the piezoelectric actuator and the magnetostrictive actuator.2. The fuel injector according to claim 1, wherein: the fuel injector isan injection valve for fuel injection equipment in an internalcombustion engine.
 3. The fuel injector according to claim 1, furthercomprising: a valve housing; a first sealing element for sealing a firstouter flange located at an end of the actuator housing from the valvehousing; and a second sealing element for sealing a second outer flangelocated at another end of the actuator housing from the valve housing.4. The fuel injector according to claim 3, wherein: the first outerflange abuts a first end face of the one of the piezoelectric actuatorand the magnetostrictive actuator, the second outer flange abuts a firstend of the compression spring, and a second end face of the one of thepiezoelectric actuator and the magnetostrictive actuator and a secondend of the compression spring are supported on a middle flange.
 5. Thefuel injector according to claim 4, further comprising: an operatingbody that is in touch with the valve needle and is firmly connected tothe middle flange.
 6. The fuel injector according to claim 4, wherein:the actuator housing with the first outer flange borders on aring-shaped first damping chamber filled with a damping medium, and theactuator housing with the second outer flange borders on a ring-shapedsecond damping chamber filled with the damping medium.
 7. The fuelinjector according to claim 6, further comprising: a fuel inlet; and aguide slot, wherein: the first damping chamber and the second dampingchamber are in contact with the fuel inlet via the guide slot partiallythrottled.
 8. The fuel injector according to claim 7, wherein: aquasi-static positional change of the actuator housing mediated by themiddle flange and caused by a thermal change of a length of the one ofthe piezoelectric actuator and the magnetostrictive actuator is offsetby volume compensation in the first damping chamber and the seconddamping chamber in that the damping medium one of flows in and escapesvia the guide slot.
 9. The fuel injector according to claim 6, wherein:the actuator housing is axially freely, slidingly movable subject tooppositely changing volumes of the first damping chamber and the seconddamping chamber.
 10. The fuel injector according to claim 6, wherein:the damping medium is a fuel flowing through the fuel injector.
 11. Thefuel injector according to claim 1, further comprising: an operatingbody, wherein: the one of the piezoelectric actuator and themagnetostrictive actuator is formed ring-shaped and includes a centralrecess in which the operating body acts upon the valve needle.